No because you just wouldn't want to, or No because it's a deeper involvement, different from a Carol Service?
I go to enjoy the carols and to watch the ceremony (and to have some mince pies and punch afterwards) but I don't participate in worship: I don't recite the Creed or take communion, for instance. To me, attending is whatever the religious equivalent of neighbourly is, whereas taking communion would be blasphemous.
TYWD